Thermostatic working element having an electric heating element

ABSTRACT

In order to arrange an electric heating element in a housing of a thermostatic working element and to guide connecting lines to the outside in a sealing manner, a base made of plastic is injection molded into an opening of the bottom through which the connecting lines are guided to the outside.

This is a divisional application of application Ser. No. 08/587,946,filed Jan. 17, 1996, now U.S. Pat. No. 5,678,300.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to a thermostatic working element having ahousing for receiving an expansion medium in which an electric heatingelement is arranged which is provided with connecting lines which areguided to the outside in a base which surrounds them and closes anopening of the bottom of the housing, and to a process for bringing anelectric heating element into a housing.

In particular, such a thermostatic working element is used particularlywith a thermostatic valve as it is known from German Patent Document DE42 33 913 A1.

An electrically heated, thermostatic working element is known (EuropeanPatent Document EP 0 139 586 A1) in which an opening of the bottom ofthe housing is closed by means of a base made of plastic which surroundsthe connecting lines of the heating element and through which theconnecting lines are guided to the outside. The base is produced as aseparate component. It is inserted from the outside into an opening ofthe housing having a ring shoulder with the interposition of a sealingring and is held by means of a flanging of the outer edge of theopening.

It is an object of the invention to provide a construction which is assimple as possible and offers a high measure of tightness against anemerging of the expansion medium.

This object is achieved in that the base is injected molded into theopening of the bottom of the housing.

The mounting of an injected base has the advantage that the base isalready mounted when it is manufactured without requiring any additionalmounting operations for bringing in and adapting the base. In addition,such an injected base, in a simple manner, can be designed such that avery high measure of tightness is obtained.

According to certain preferred embodiments of the invention, it isprovided that the base injected into the bottom projects to the outsideby means of a projection surrounding the connecting lines. As a result,it is achieved that, on the one hand, the connecting lines aresurrounded by the injected base along a relatively large length whichleads to a high measure of tightness while, on the other hand, theconnecting lines are held in a very secure manner so that the fasteningpoints between the connecting lines and the heating element are relievedfrom tensile forces which are exercised on the connecting lines.

In a further development of preferred embodiments of the invention, itis provided that the injected-molded-on base frames an edge of theheating element which faces the bottom of the housing. As a result, theheating element is also held by the injected base and is fixed in thehousing.

In an expedient further development of preferred embodiments of theinvention, it is provided that the base covers the bottom in theinterior of the housing. Thus, relatively large sealing surfaces areobtained between the base and the housing. For the same purpose, it isprovided in another embodiment that, in the interior of the housing, thebase covers an edge area of the interior wall of the housing whichadjoins the bottom.

In a further development of preferred embodiments of the invention, itis provided that the opening of the bottom is provided with at least onesurrounding annular groove which is filled by the material of theinjected base. This results in the form-locking connection between theinjected base and the housing while, in addition, the sealing surfacesare enlarged once again.

In a further development of preferred embodiments of the invention, itis provided that the base injected into the opening of the bottom of thehousing is made in one piece with a cap framing the housing on theoutside. By means of such a molded-on cap, the tightness can be improvedfurther, on the one hand, while, on the other hand, the effectivesensing surface of the housing of the thermostatic working element canbe determined by dimensioning the axial length of the cap. In the caseof an advantageous further development, it is provided that the cap isequipped with at least one receiving device for an additional element.Such an additional element may, for example, be a sealing ring or thelike.

In a further development of preferred embodiments of the invention, itis provided that the area of the base facing the interior of the housingis provided with a sealing mass adjoining the interior wall of thehousing and/or the outer surfaces of the supporting body. This sealingmass, which is a preferably adhesive plastic material which can bepolymerized out, results in a further increase of the tightness by meansof the additional sealing mass which has permanently elasticcharacteristics and which ensures the tightness also for an extendeduseful life of the thermostatic working element.

In a further development of preferred embodiments, the invention relatesto a process for bringing an electric heating element into a housing ofa thermostatic element which is characterized in that the heatingelement provided with the connecting lines is held in a core whichembeds it and is introduced into the housing together with the core, inwhich case the core, the housing and a mold part are joined to form acasting mold into which a base made of plastic is injected which closesthe recess of the bottom and surrounds the connecting lines.

In a further development of preferred embodiments of the invention, itis provided that, before the injection of the base, the walls of thehousing and/or the surface of the heating element are provided with anadhesion promoting substance by spraying or otherwise applying theadhesive promoting substance. This adhesion promoting substance has theresult that an adhesive connection is provided between the injected baseand the walls of the housing and/or the supporting body of the heatingelement.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial sectional view of a housing of a thermostaticworking element with a heating element and an injected base constructedaccording to a preferred embodiment of the invention, in which case thecasting mold created for the injecting and supplemented by the housingis shown by a dash-dotted line;

FIG. 2 is a partial sectional view of a housing of a thermostaticworking element constructed according to another preferred embodiment ofthe invention and having a base which forms a flap framing the housingin its operating area;

FIG. 3A is a partial sectional schematic view showing a clamping chuckwith a tong-shaped clamping element for holding a supporting body of anelectrical heating element during casting of preferred embodiments ofthe present invention; and

FIG. 3B is a side view of the clamping tongs of the clamping assembly of3A.

DETAILED DESCRIPTION OF THE DRAWINGS

The housing 10, which is enlarged approximately 20 times in the drawing,is made of metal. It has a pot-shaped design with a bottom and an openside which is not shown. The open side is normally closed by means of aguiding part for a working piston, in which case a bag-type membrane isprovided between the guiding part and the housing, which membranereceives the working piston. Inside the housing, an expansion medium isarranged, particularly a wax mixture which, in a temperature range whichcan be defined by the mixture of the wax, changes its state ofaggregation and drives out the working piston.

An electric heating element 11 is also arranged inside the housing whichconsists of a plate-shaped supporting body to which a meandering heatingresistance in the form of a layer is applied which is not shown. Twoconnecting lines 12 are soldered to the heating resistance and areguided to the outside through an opening 13 of the bottom of the housing10. The connecting lines 12 are soldered to the heating resistance in astepped area 14 which has a smaller transverse dimension than opening 13and which reaches into the opening 13 of the bottom of the housing 10.The opening 13 is also provided with a surrounding annular groove 15.

The opening 13 of the bottom of the housing 10 is closed by an injectedbase 17 made of plastic. This base 17 fills the annular groove 15 andcovers the bottom and the lower edge area of the interior wall of thehousing 10. In this case, injected base 17 also frames the lower edge ofthe supporting body 11 of the electric heating element and particularlythe projection 14 which has the soldering points for the connectinglines 12. The base 17 has a projection 18 which projects out of thebottom of the housing 10 and surrounds the connecting lines 12 which,with a portion of their insulations 19, are also still surrounded by thebase 17. The exterior ends of the connecting lines 12 are free of theinsulation and are wired and galvanized.

In order to be able to produce the base 17, a casting mold is made whichis partially formed of the housing 10. The supporting body 11 is fittedinto a recess of a core 20 corresponding to the inside contour of thehousing 10 such that supporting body 11 projects out of the core 20 bymeans of its lower edge area and the projection or stepped section 14with the soldering points of the connecting lines 12. The core 20 isfitted into the housing 10 in which case it is sealingly supported on acollar 21 of the housing 10. A mold part 22 is assigned to the exteriorside of the bottom of the housing 13 and is connected with a recess 23for the projection 18. This mold part 22 preferably consists of twoparts which are divided in the plane of the drawing and which are eachprovided with two half-shell-shaped recesses 24 for leading out theconnecting lines 12 provided with the insulations 19. Since the core 20is supported on the collar 21, a sufficient closing force can be appliedbetween the mold parts 22 and the core 20. In a manner which is notshown, the mold parts 22 contain the injection openings through whichthe injection of the plastic material which forms the base 17 takesplace.

In order to hold the supporting body 11 with the heating resistance sotightly in the core 20 that, during the injection process, no plasticenters the area of the recess receiving the supporting body 11, it isexpediently provided that the core 20 is provided with a tong-shapedclamping element. The tong-shaped clamping element consists of at leasttwo halves which are provided with U-shaped recesses and which clamp theflap-shaped supporting body 11 between one another. The clamping of theclamping element takes place by means of conical surfaces.

FIGS. 3A and 3B depict a tong-shaped clamping element that can be usedin holding the supporting body 11 during molding operations. Thisclamping assembly is generally similar to a conventional machine toolchucking assembly, with a special configuration to accommodate the shapeof the supporting body 11 being held, and to accommodate the moldingprocess described herein. The tong-shaped chucking element includes anouter shell part 31 which is insertable into the housing 10 to aposition where its rim or edge 32 is abuttingly supported at the collar21 on housing 10 in FIG. 1 or collar 21' in housing 10' in FIG. 2. Theend section of outer shell 31 adjacent the edge 32 has an inner conicalsurface 33. Inside the housing 31 there is a shaft or rod 34 arrangedwhich has an end region provided with an axial slot 35. The end of theshaft 34 is formed with a conical section 36 which essentiallycorresponds to the inside conical surface 33 of the housing 31. When thehousing 31 and the shaft 34 are slid axially relative to one another,the cone shaped part 36 travels along the inner conical surface 33 ofthe housing 31 and elastically deforms the shaft 34 in the region of itsslot 35 so that the edge surfaces 37 of the slot 35 press against andclamp the supporting body 11.

The edge surfaces 37 extend parallel with respect to one another and lieflat against the supporting body 11. In the connecting region, the slot35 is slightly widened so that the surfaces 37 only engage on thesupporting body 11. In the end region of the surfaces 37, cutouts 38 areprovided which, during molding, result in provision of the protrusion17A as shown in the FIG. 2 embodiment. The shell or housing 31 isfurther provided with a cutout 39 which surrounds the supporting body 11in such a manner that during injection molding of the base 17', leakageof the molding material flow into the shell 31 is avoided or minimized.Subsequent to the casting operation, the tong-shaped clamping elementcan be removed by first axially displacing the housing 31 to loosen thegrip of surfaces 37, and then pulling of the clamping element out of thehousing 10'.

In the case of the embodiment according to FIG. 2, the base 17' injectedinto the bottom area of the housing 10' is provided with a cap 25 whichis produced in one piece with it and which frames the housing 10' on theoutside starting from the bottom area along a defined axial length. Thecap is provided with receiving devices 26, 27 for auxiliary devices, forexample, for sealing rings or the like. In the area of the cap 25, thehousing 10' is provided with anchoring grooves 28.

Before the injection of the base, the walls of the lower area of thehousing 10, 10' and preferably also the area of the supporting body 11around which the molding of base 17 or 17' is to take place and theconnecting wires 12 are provided with an adhesion-promoting substancewhich is suitable for an intimate connection between the plastic and themetal. Such an adhesion-promoting substance can also be applied byimmersing, spraying, rolling or coating.

As illustrated in the embodiment according to FIG. 2, it is advantageousto bring a sealing mass 30 into the interior of the housing 10', whichsealing mass 30 seals off the base 17' with respect to the interiorwalls of the housing 10' and additionally seals off the base 17' withrespect to the supporting body 11 of the heating element. In suchthermostatic working element, pressures may occur of above 100 bar. Inaddition, the usage range of such a thermostatic working element isbetween -40° C. and +150° C., particularly when it is used inconjunction with a thermostatic valve of a cooling system of aninternal-combustion engine of a motor vehicle. This sealing mass 30,which is entered in a liquid or viscous form, preferably consists of aplastic material which can be polymerized out and which is also enteredas a two-constituent mass. It is advantageous for this plastic material,such as silicone, to have permanent elastic characteristics and toestablish an adhesive connection with the plastic material of the base17' as well as to the metal of the housing 10' as well as to thesupporting body 11 which consists of ceramic material or anotherelectrically non-conducting, heat-resistant material.

It is also contemplated by the invention to arrange other electricheating elements in a corresponding manner and hold the same by means ofan injection-molded-on base, for example, pill-shaped PTC-heatingelements.

Although the invention has been described and illustrated in detail, itis to be clearly understood that the same is by way of illustration andexample, and is not to be taken by way of limitation. The spirit andscope of the present invention are to be limited only by the terms ofthe appended claims.

What is claimed is:
 1. A thermostatic working element comprising:ahousing for receiving an expansion medium, an electric heating element,having a supporting body and a resistance laver on the supporting body,arranged in said housing and provided with connecting lines, saidhousing including a bottom opening for accommodating passagetherethrough of the connecting lines, and an injected base made ofplastic injection molded into the bottom opening of the housing so as tosurround the connecting lines and a lower edge of said supporting body,securely hold the connecting lines, and close the bottom opening of thehousing.
 2. Thermostatic working element according to claim 1, whereinthe base injected into the bottom opening includes a projection whichprojects toward the outside and surrounds the connecting lines. 3.Thermostatic working element according to claim 2, wherein theconnecting lines are provided with insulation which projects into theprojection of the base.
 4. Thermostatic working element according toclaim 1, wherein the lower edge of the supporting body faces the bottomof the housing.
 5. Thermostatic working element according to claim 1,wherein the injected base covers the bottom interior of the housingwhich surrounds the bottom opening.
 6. Thermostatic working elementaccording to claim 5, wherein the injected base covers an edge area ofthe interior wall of the housing which adjoins the bottom interior. 7.Thermostatic working element according to claim 1, wherein the bottomopening is provided with at least one surrounding annular groove whichis filled by the material of the injected base.
 8. Thermostatic workingelement according to claim 1, wherein the connecting lines are connectedby soldering points with said resistance layer of the electric heatingelement which are situated inside the injected base.
 9. Thermostaticworking element according to claim 1, wherein the injected base isintegrally formed in one piece with a cap framing the housing on theoutside.
 10. Thermostatic working element according to claim 9, whereinthe cap is provided with at least one receiving recess for receiving anauxiliary sealing element.
 11. Thermostatic working element according toclaim 1, wherein an area of the base facing the interior of the housingis provided with a sealing mass which adjoins at least one of theinterior wall of the housing and outer surfaces of the electric heatingelement.
 12. Thermostatic working element according to claim 11, whereinthe sealing mass is a preferably adhesive plastic material which can bepolymerized out.
 13. Thermostatic working element according to claim 3,wherein the lower edge of the supporting body faces the bottom of thehousing.
 14. Thermostatic working element according to claim 4, whereinthe injected base covers the bottom interior of the housing whichsurrounds the bottom opening.
 15. Thermostatic working element accordingto claim 14, wherein the injected base covers an edge area of theinterior wall of the housing which adjoins the bottom interior. 16.Thermostatic working element according to claim 15, wherein the bottomopening is provided with at least one surrounding annular groove whichis filled by the material of the injected base.
 17. Thermostatic workingelement according to claim 16, wherein an area of the base facing theinterior of the housing is provided with a sealing mass which adjoins atleast one of the interior wall of the housing and outer surfaces of theelectric heating element.